1. Field of the Invention
The present invention relates to a device for controlling temperature of a proximal portion of a heating cylinder of an injection molding machine.
2. Description of Related Art
An injection molding machine has a mold clamping mechanism, an injection mechanism and an operation panel, all arranged on a frame, and performs injection molding by clamping a mold between stationary and movable plates constituting the mold clamping mechanism, sliding the injection mechanism to press a nozzle at a distal end of a heating cylinder into a center hole of the stationary plate, and injecting molten resin from the nozzle to be molded in a cavity defined in mold halves.
The temperature of an injection screw in the injection molding machine affects the conveyance of the resin in a metering process as well as the hysteresis of the resin. In order to properly convey the resin in the metering process, therefore, the temperature of the injection screw needs to be controlled such that the resin is prevented from adhering to the outer peripheral surface of the injection screw, and that resin introduced from a hopper is melted at the nozzle side, and not at a lower portion of the hopper. For such temperature control, a temperature control device is provided for controlling the temperature of the proximal portion of the heating cylinder.
The temperature control device is designed to control the temperature of the proximal portion of the heating cylinder by simply allowing a temperature control medium to flow downward. The flow rate of the temperature control medium is, conventionally, not controlled at all or is controlled by means of a main tap or a manual flow control valve arranged in the middle of the medium line.
If the flow rate of the temperature control medium is not controlled at all, the temperature of the proximal portion of the heating cylinder becomes unstable and the plasticizing ability of the resin lowers due to excessive removal of heat from the resin, giving rise to a problem that many defective articles are produced because of uneven molding conditions.
Also, even in the case where the temperature control is performed by means of a manual flow control valve, the operation for such temperature control is troublesome because the flow control valve is located on the side of the injection molding machine opposite the operation panel or at a distance from the injection molding machine, and thus a problem arises in that the operator is forced to work in a small dangerous place such as at the back of the machine.
In view of the above problem of low operation efficiency, a method has been proposed in which the control valve is arranged near the operation panel (e.g., in Examined Japanese Utility-Model Publication No. 7-27148). In factories, however, a main tap of the medium is usually fixed in position and it is necessary that piping be installed between the injection molding machine and the main tap. Accordingly, the degree of freedom in installing the piping is low, and in addition, the cost increases because of the use of parts for fixing the piping Ad the flow control valve, and also because of work associated therewith.
Also, a mechanism for preventing the plasticizing ability of resin from being lowered due to excessive removal of heat from the resin has been proposed, in which the temperature control device for controlling the temperature of the proximal portion of the heating cylinder has a two-upper/lower-piece structure (e.g., Unexamined Japanese Patent Publication No. 7-232361). FIG. 11 is a diagram illustrating such a device with the two-upper/lower-piece structure. In FIG. 11, a temperature control device 100 for controlling the temperature of the proximal portion of the heating cylinder comprises two, upper and lower separate jackets 101 and 102, and a proximal portion 106 of the heating cylinder having an injection screw 104 inside is fixed in position between the jackets 101 and 102. One of the jackets, that is, a jacket 101 has a communication port 105 formed therethrough for introducing resin.
A portion of this device disposed in contact with the heating cylinder proximal portion has a semicylindrical surface and thus is difficult to machine with high accuracy. Even if the temperature control device is fixed by bolts or the like, it is still associated with a problem that the efficiency of heat transfer and thus the temperature controllability are low because of a small area of contact between the heating cylinder proximal portion and the temperature control device. Also, since the contact area between the proximal portion of the heating cylinder and the temperature control device varies depending upon a skill of a person who installs the temperature control device, molding conditions vary from machine to machine, and in addition, temperature distribution is liable to become uneven between the upper and lower pieces of the temperature control device, which exerts adverse effects on the molding conditions.
An electromagnetic valve may be used to control the flow rate of the temperature control medium. In this case, however, a controller and a temperature sensor are required in addition to the electromagnetic valve, and thus a problem of high cost arises despite the advantage of high-accuracy temperature controllability.
Further, in order to prevent excessive temperature change from being caused by the downflow of a large quantity of the temperature control medium in a short time, a passage through which the temperature control medium flows may be reduced in diameter. In this case, however, impurities contained in industrial water adhere to the inner surface of the passage, and therefore, frequent maintenance is required to eliminate clogging of the passage with waste, rust, water scale, etc.
FIG. 12 is a sectional view illustrating the arrangement of another conventional device for controlling the temperature of the proximal portion of the heating cylinder. In FIG. 12, a temperature control device 110 comprises a jacket 111 having a hole 112 into which the proximal portion of the heating cylinder is inserted, a passage 113 is formed in the jacket 111 for passing a temperature control medium therethrough, and a communication port 115. The conventional passage often has a complex route for the purpose of temperature control, and it is therefore necessary to cut machining holes for forming the passage. Since such machining holes are unnecessary for actual operation of the passage, a large number of plugs 114 are used to close the holes. Accordingly, foreign matter is liable to be deposited inside the passage, and the removal of the deposited matter requires prolonged maintenance work, often necessitating detachment of the heating cylinder.
An object of the present invention is to improve maintainability and reduce a manufacturing cost of a temperature control device of a proximal portion of a heating cylinder of an injection molding machine. Another object of the present invention is to make it easy to check and control the flow rate of a temperature control medium.
A temperature control device of the present invention introduces improvements in an attaching structure of the device to the proximal portion of the heating cylinder and an arrangement of a passage of heat medium so as to enhance the maintainability and reduce the manufacturing cost. Further, a flow-rate control mechanism and a flow-rate detecting mechanism are arranged such that an operator can check and control the flow rate at a location where an ordinary operation of an injection molding machine is performed, thereby the flow rate of the heat medium can be checked and controlled with ease.
A temperature control device for a heating cylinder of an injection molding machine according to the present invention comprises a jacket to be attached to a proximal portion of the heating cylinder of the injection molding machine. The jacket has at least one pair of through holes for flowing heat medium for temperature control. These through holes are connected by pipes so that a passage for the heat medium is formed by the through holes and the pipes. A flow-rate control mechanism for controlling flow rate of the heat medium flowing in the passage and a flow-rate detection mechanism for detecting flow rate of heat medium are arranged in the passage formed by the pipes.
The passage for the heat medium in the jacket is formed by simple through holes, and thus can be formed by a simple machining operation. Also, since the passage is formed by through holes, deposit adhered to the inner surface of the passage can be easily removed without detaching the jacket from the proximal portion of the heating cylinder, whereby maintainability can be improved.
The flow-rate control mechanism may comprise a control valve arranged in the passage and a control knob for varying the opening of the control valve. The opening of the control valve is varied by means of the control knob to vary the diameter of the passage, whereby the flow rate of the temperature control medium flowing in the passage is controlled. The flow-rate detection mechanism may comprise a floating member urged by a spring arranged inside the passage and an indicator interlocking with movement of the floating member to visually indicate the flow rate of the heat medium flowing in the passage. The flow-rate control mechanism and the flow-rate detection mechanism may be formed integrally to have a single body or separately to have separate bodies.
Neither the flow-rate control mechanism nor the flow-rate detection mechanism requires an electromagnetic valve, a controller for actuating the electromagnetic valve and a sensor, so that the manufacturing cost can be reduced. In the case where high-accuracy temperature control is required, an electromagnetic valve may be used in combination to finely control the flow rate of the heat medium.
The flow-rate control mechanism and the flow-rate detection mechanism are arranged near the jacket to make it easy to attach these mechanisms to the jacket and thereby pipes connecting these mechanisms can be shortened to facilitate piping work.
The through holes in the jacket are arranged to extend from one side of the jacket on which an operation panel of the injection molding machine is positioned to the opposite side of the jacket. The flow-rate control mechanism and the flow-rate detection mechanism are connected, by pipes, to openings of the through holes which open on the side of the jacket on which the operation panel is located, whereby these mechanisms are situated on the same side as the operation panel of the injection molding machine.
With the above arrangement, an operator can control and confirm the flow rate at a location where the operator performs an ordinary operation of the injection molding machine on the operation panel.
A pipe for supplying the heat medium to the passage and a pipe for discharging the medium from the passage are attached to the other openings of the through holes on the jacket on the other side opposite to the side where the operation panel of the injection molding machine is located. Thus, all openings of the through holes are used for the attachment of the flow-rate control and detection mechanisms and the supply and discharge pipes, to eliminate the use of plugs.
The flow-rate control mechanism, the flow-rate detection mechanism, the supply pipe and the discharge pipe can be easily attached and detached through, for example, a flange or screw mechanism, without the need to detach the heating cylinder etc. Further, the present invention does not require the use of special piping or devices for mounting the flow-rate control mechanism or flow-rate detection mechanism on the same side as the operation panel, or the use of fixing parts such as metal plates, whereby the assemblage of the injection molding machine is simplified and the number of parts is reduced, thereby reducing the cost.
Further, the jacket for temperature control can be manufactured by simple machining operation of forming a hole for inserting the heating cylinder, through holes for passing the heat medium and a communication port for introducing resin in one workpiece. Also, the temperature control can be performed without the need to narrow the passage in the jacket, whereby clogging of the passage and thus frequency of maintenance can be reduced.
The heat medium for temperature control is introduced from the supply pipe into the passage in the jacket from the side of the injection molding machine opposite to the side where the operation panel is located, and after heat exchange is performed in the passage, the medium is introduced to the flow-rate control mechanism and the flow-rate detection mechanism arranged on the side of the injection molding machine where the operation panel is located. An operator can check and control the flow rate of the heat medium by means of the flow-rate detection mechanism and the flow-rate control mechanism. Then, the heat medium is again introduced into the passage in the jacket from the side where the operation panel is located, and after the heat exchange in the passage the medium is discharged through the discharge pipe from the side opposite to the operation panel. In the jacket, supply and discharge passages can be formed for the flow-rate control and detection mechanisms by a pair of through holes, and one pair or a plurality of pairs of through holes may be provided for these passages.